This article is based on John Dawson’s inaugural professorial lecture at the University of Otago, on September 6, 2007. It concerns how we should think about the personal liberty, or freedom, of people with serious mental illness and why this is important for the design of our mental health laws. The author focuses on laws that authorise the use of compulsory psychiatric treatment outside hospital, under what are known as Community Treatment Orders. The article concludes that the mental health laws of New Zealand and Australia reflect a humane form of liberalism, consistent with the political culture and constitutional traditions of these nations.